Implied probability
As of 13 June 2026, implied probability is the chance of an outcome as expressed by betting odds, converted into a percentage. For decimal odds, it is simply 1 ÷ odds. Because bookmakers add a margin, the implied probabilities across a market add up to more than 100% — the extra is the operator's built-in edge. Information only, not betting advice. 18+.
Updated · ScoreGPT
How do you calculate implied probability?
Implied probability is calculated straight from the odds, and the formula depends on the odds format — the table below covers all three.
| Odds format | Example | Implied probability |
|---|---|---|
| Decimal | 2.50 | 1 ÷ 2.50 = 40% |
| Fractional | 6/4 | denominator ÷ (denominator + numerator) = 4 ÷ 10 = 40% |
| American (+) | +150 | 100 ÷ (150 + 100) = 40% |
| American (−) | −150 | 150 ÷ (150 + 100) = 60% |
So odds of 2.50 imply the bookmaker is pricing that outcome at roughly a 40% chance.
Why do implied probabilities add up to more than 100%?
Because bookmakers build a margin into every market, the implied probabilities across all outcomes sum to more than 100% — usually around 105%. That extra ~5% is the bookmaker's margin (also called the overround or vig). It is how the operator builds in profit, and it is why, on average, the odds are slightly worse than the "true" probabilities.
This margin is the core reason the maths favours the operator over time, and it is essential context for value betting: you are not comparing your estimate to the true chance, but to a margin-inflated one.
Why does implied probability matter for AI predictions?
Implied probability turns odds into a percentage you can compare directly with a model's output. If an AI model estimates a 50% chance and the odds imply 40%, the difference is what some tools flag as "value." ScoreGPT's models produce their own probability estimates per match, which can be read alongside market-implied probabilities.
Converting odds to a percentage is a neutral, descriptive calculation — it is information, not a recommendation to bet. 18+.
Frequently asked
▸How do I convert decimal odds to a percentage?
Divide 1 by the decimal odds, then multiply by 100. Odds of 2.50 give 1 ÷ 2.50 = 0.40, or 40%. Odds of 1.50 give 1 ÷ 1.50 ≈ 66.7%.
▸Why do the percentages add up to over 100%?
Bookmakers add a margin (the overround or vig), so the implied probabilities across a market exceed 100%. The extra is the operator's built-in edge — the reason the maths favours the operator over time.
▸Is implied probability the real chance of an outcome?
Not exactly. It is the chance the odds express, inflated by the bookmaker's margin. The "true" probability is unknown; implied probability is the market's margin-adjusted estimate, not a fact.
▸Is calculating implied probability betting advice?
No. It is a neutral way to read odds as percentages — information only, not a recommendation to place any bet. If you choose to gamble, do so responsibly. 18+.
AI predictions are for information and entertainment only — not betting advice. 18+. Please gamble responsibly.